Communication method and system

ABSTRACT

A method of co-ordinating communication between a plurality of base stations in a communication system, comprising designating timeslots where said base stations receive and/or transit co-ordination messages to each other. The system may be an autonomous cellular system and the timeslots may be regularly spaced.

CROSS-REFERENCE TO A RELATED PATENT APPLICATION

This patent application is a continuation of U.S. patent applicationSer. No. 13/127,779, filed May 16, 2011, which claims priority toInternational Application No. PCT/EP2008/065014 filed Nov. 5, 2008.

FIELD OF THE INVENTION

This invention relates to communications systems and has particular butnot exclusive application to local areas (e.g. autonomous) cellularcommunications systems.

BACKGROUND TO THE INVENTION

A proposal for LTE-A (Long Term Evolution Advanced) radio systems isautonomous component carrier selection. In such systems, an arrangementof base stations in a communication system such as a cellularcommunication system, also referred alternatively as Node B's, operategenerally without central control. Conventional systems generallyinclude a network controller for example.

This enables cheap uncoordinated deployment of Node Bs in local areaenvironments. More details for this can be found in on-line documentsR1-083733 and R1-083103 at http://www.3gpp.org.

An autonomous component carrier selection scheme has been proposed whichrelies on a concept where each cell automatically selects one of thecomponent carriers as its primary carrier (also some-times called thebase carrier). The primary/base carrier is assumed to be used forinitial connection of User Equipment e.g. terminals in the cell.Depending on the offered traffic in a cell and the mutual interferencecoupling with the surrounding cells, transmission/reception on allcomponent carriers may not always be the best solution. It is thereforeproposed that each cell dynamically selects additional componentcarriers for transmission/reception as well. The latter is referred toas selection of secondary component carriers (also some-times calledextended carriers). All component carriers not selected for primary orsecondary are completely muted (uplink/downlink) and not used by thecell. In order to have efficient autonomous component carrier selectionat each Node B (also referred to alternatively as a base station or aneNB in 3GPP terminology, some information from the neighbouring Node Bsis also needed by an Node B, and this information is assumed to beavailable via inter Node B over-the-air communication (OTAC) for caseswhere there is no X2 between the Node Bs (i.e., meaning Home/Femto NodeB cases). X2 is a common interface between eNodeB's. One of the majorchallenges for inter Node B OTAC is how to coordinate suchtransmissions/receptions among the Node Bs, which are within the samelocal area cluster. The latter is assumed to be the case for both FDDand TDD. However, a Node B may be able to receive multiple OTAC messagesfrom different Node Bs at the same time if these are sent on differentcomponent carriers. If the OTAC messages use a cell-specificscrambling/spreading component, it might even be possible to receivemultiple OTAC messages within the same component carrier at the sametime. There is a requirement to provide an accurate method forcoordinating the transmission and reception of OTAC messages. Theinvention provides for Node Bs to send OTAC messages. The invention alsoprovides rules for when Node Bs have to be in Discontinuous reception(DTX) for reception of potential OTAC messages by other Node Bs in theclose vicinity.

STATEMENT OF THE INVENTION

According to a first aspect of the invention there is provided a methodof co-ordinating communication between a plurality of base stations in acommunication system, comprising designating and or synchronisingtimeslots where said base stations receive and/or transit information toeach other.

The information may pertain to co-ordination of said base stations. Theinformation may be OTAC messages.

The base station may be part of a cellular communication network, suchas an autonomous network.

Preferably the timeslots are regularly spaced.

In a preferred embodiment the timeslots are a function of system framenumber (SFN).

In an alternative preferred embodiment the timeslots may be based onmonitoring and adopting the patterns of neighboring base stations.

In an embodiment, the method includes determining if the base stationhas a message to transmit, and if not it listening to potential messagescoming from other base stations.

Another embodiment includes determining if a base station has aco-ordination message to be transmitted, and if so transmitting theinformation in the first coming timeslot.

The information may be retransmitted automatically. In another preferredembodiment, the information may be retransmitted after N timeslotsperiods. N may be a (pseudo) random integer. In one embodiment N may bedifferent from and varies between different base stations. N may bebased on base station ID.

According to a second aspect of the invention there is provided acomputer readable medium comprising a computer program thereon, saidcomputer program performing the methods of the invention.

According to a third aspect of the invention a base station adapted toreceive and/or transit information to or from one or more other basestations during designating and/or synchronised time slots.

The information may pertain to co-ordination of a plurality of basestations in a communication system, such as an autonomous cellularcommunication system.

According to a fourth aspect of the invention there is provided acommunication system comprising a plurality of base stations, said basestations adapted to receive and/or transit information to or from one ormore other base stations during designating and/or synchronisedtimeslots.

SUMMARY OF FIGURES

For a better understanding of the present invention and how the same maybe carried into effect, reference will now be made by way of exampleonly and to the accompanying drawings in which:

FIG. 1 shows schematically a conventional LTE system.

FIG. 2 shows elements the system of FIG. 1 in more detail.

FIG. 3 Simple illustration of a local area autonomous system with fiveeNode Bs having OTAC wherein an embodiment of the invention may beutilised.

FIG. 4 shows an example of component carriers forming which may beutilised with the FIG. 3 system.

FIG. 5 shows an illustration of one embodiment of the invention whereregular periodic time pattern where Node Bs listens for or sends OTACmessages.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Before explaining in detail a few exemplifying embodiments, a briefexplanation of wireless access is given with reference to FIG. 1 whichshows a conventional communication system 1 providing wirelesscommunications to a plurality of communication devices 2. Thecommunication device, for example a mobile user device or equipment, canbe used for accessing various services and/or applications provided viathe wireless communication system. The communication device cantypically access wirelessly a communication system via at least onewireless transmitter and/or receiver Node B 3 of an access system.Non-limiting examples of access nodes are a base station of a cellularsystem, for example a 3G WCDMA Node B, a base station of a wirelesslocal area network (WLAN) and a satellite station of a satellite basedcommunication system.

The communications may be arranged in various manners based on anappropriate radio access technology or technologies. The access isprovided via radio channels also known as access channels. Eachcommunication device 1 may have one or more radio channels open at thesame time. Each communication device may be connected wirelessly to morethan one base station 3 or similar entity. Also, a plurality ofcommunication devices may communicate with a base station or similar,and/or attempt to access the communication system via the same basestation. A plurality of communication devices may also share a channel.For example, to start communications or to connect to a new accesssystem, a plurality of communications devices may attempt to make theinitial contact via a single channel, for example via a random accesschannel (RACH). The attempts to access may be made substantially at thesame time.

The base station (eNode B) can be connected to other parts of thecommunication system via appropriate connections, for one or moreappropriate gateway nodes. The eNode B 3 has an antenna forcommunicating with the user equipment via wireless link. The eNode B hasa data processing entity for carrying out various processes.Additionally a memory is provided which stores information which is usedby the eNode B. A base station is typically controlled by at least oneappropriate controller apparatus, e.g. network controller, generallydenoted by 4 and can be provided for managing of the operation of thebase station and/or communications via the base station. The controllerapparatus is typically provided with memory capacity and at least onedata processor. Various functional entities may be provided in thecontroller by means of the data processing capability. The functionalentities provided in the base station controller may provide functionsrelating to radio resource control, access control, packet data contextcontrol, relay control and so forth.

A user device 2 can be used for various tasks such as making andreceiving phone calls, for receiving and sending data from and to a datanetwork and for experiencing, for example, multimedia or other content.For example, a communication device may access applications provided viaa telephone network and/or a data network, such as applications that areprovided based on the Internet Protocol (IP) or any other appropriateprotocol. An appropriate mobile communication device may be provided byany device capable of at least sending and/or receiving wireless signalsfrom the access system. Non-limiting examples include a mobile station(MS) such as a mobile phone or a smart phone, a portable computerprovided with a wireless interface card or other wireless interfacefacility, personal data assistant (PDA) provided with wirelesscommunication capabilities, or any combinations of these or the like.The communication device 1 is typically provided with appropriate dataprocessing apparatus.

FIG. 2 shows in more detail the system of FIG. 1 and shows thisarchitecture only to give an example of a possible communication systemwhere the embodiments described below may be provided and that otherarrangements and architectures are also possible. For example, the userdevice may communicate with a different access system. The eNode B 3 hasan antenna 5 for communicating with the user equipment via wirelesslink. The eNode B has a data processing entity 6 for carrying outvarious processes. Such processes may include some embodiments of theinvention. Additionally a memory 7 is provided which stores informationwhich is used by the eNode B. It is noted that the embodiments of theinvention and functionality may be provided according to someembodiments of the invention by a separate component to the dataprocessing entity. In some embodiments the functionality of the methodsaccording to some embodiments of the invention are carried out by otherparts of a system separate from the node B. For example in an embodimentthe functionality may be carried out by network controllers.

The mobile device may communicate via an appropriate radio interfacearrangement of the mobile device. The interface arrangement may beprovided for example by means of a radio part 8 and associated antennaarrangement. The antenna arrangement may be arranged internally orexternally to the mobile device. A mobile device is typically providedwith at least one data processing entity 9 and at least one memory 10for use in tasks it is designed to perform. The data processing andstorage entities can be provided on an appropriate circuit board and/orin chipsets. This feature is denoted by reference 11. The user maycontrol the operation of the mobile device by means of a suitable userinterface such as key pad 12, voice commands, touch sensitive screen orpad, combinations thereof or the like. A display 14, a speaker and amicrophone are also typically provided. Furthermore, a mobile device maycomprise appropriate connectors (either wired or wireless) to otherdevices and/or for connecting external accessories, for examplehands-free equipment, thereto. A modulator component 13 is also shown.

Some embodiments of this invention are related to the long termevolution (LTE) of 3GPP. In the proposed LTE structure the base stationis called eNode B. The physical layer is based on SC FDMA (singlecarrier division multiple access) for the Uplink and OFDMA (orthogonalfrequency division multiple access) for the downlink.

Certain embodiments can be used in a long term evolution (LTE) radiosystem. The long term evolution (LTE) is a system which provides anevolved radio access system that is connected to a packet data system.Such an access system may be provided, for example, based onarchitecture that is known from the Evolved Universal Terrestrial RadioAccess (E-UTRA) and based on use of the Evolved Universal TerrestrialRadio Access Networks (E-UTRAN) Node Bs (eNode Bs). An Evolved UniversalTerrestrial Radio Access Network (E-UTRAN) consists of E-UTRAN Node Bs(eNode Bs) which are configured to provide base station and controlfunctionalities. For example, the Node Bs nodes can provideindependently radio access network features such as user plane radiolink control/medium access control/physical layer protocol (RLC/MAC/PHY)and control plane radio resource control (RRC) protocol terminationstowards the user devices.

FIG. 3 shows a schematic example of a particular type of autonomouscellular communication system.

The autonomous system or network includes a plurality of Node B's 3,whose main function is to communicate and serve User Equipment, such asmobile telephones (not shown) in their respective cells. The basestations communicate with each other via OTAC. Such a system may embodyembodiments of the invention. It may employ an autonomous componentcarrier selection scheme. Such a system is similar to that describedabove, except that there is no central co-ordinated control. Such assystem may operate in both FDD and TDD mode, and is mainly estimated toprovide performance benefits in local area environments such as indoorscenarios, and outdoor hotspot areas with dense deployment of pico/microcells. However the invention and embodiments are not limited to this.Such systems typical may employ autonomous eNode-B component carrierselection concept for LTE-Advanced. The basic idea is that each cellselects at least one active component carrier. Secondly, cellsdynamically select additional component carriers, depending on theoffered traffic conditions, radio conditions, etc. Component carriersnot being selected by a cell may be muted, i.e. no transmission of anyuplink/downlink channels and reference symbols is performed. Theproposed concept essentially provides a simple autonomous self adjustingfrequency reuse mechanism for LTE-Advanced, which is consideredespecially beneficial for local area environments such as outdoormunicipal hot spot areas and indoor pico cell cases with uncoordinated(home) eNode-B deployment.

In a typical system, the LTE-Advanced system bandwidth is assumed toconsist of a number of separate component carriers. In the example ofFIG. 3 where there are 5 base stations, with 100 MHz system bandwidth, 5component carriers of 20 MHz are generally assumed. Assuming a bandwidthconfiguration with M=5 component carriers of e.g. 20 MHz bandwidth, eachof the 5 Node Bs will have selected different component carriers fortheir primary. This means that if for instance a Node B is silent, thenit is in principle able to receive parallel OTAC messages sent from allother Node Bs on different component carriers. However, assumingrealistic filtering and transceiver implementation, a Node B cannotreceive on one component carrier while at the same time transmitting onother component carriers. However, other configurations such as e.g. 4component carriers of 10 MHz, or sets of component carriers withdifferent bandwidth sizes could be configured as well according toembodiments of the invention. A Rel'8. A Rel'8 terminal is a UE which isproduced according to the 3GPP LTE Release 8 specifications. For LTE-Ait is envisioned that backwards compatibility should be maintained, suchthat Rel'8 UEs should still be able to operate, even that the network isupgraded to higher releases terminal is assumed to be served by a singlecomponent carrier, while LTE-Advanced terminals can be servedsimultaneously on multiple component carriers.

In one configuration, each cell automatically selects one of thecomponent carriers as its primary carrier (also some-times called thebase carrier). The primary/base carrier is assumed to be used forinitial connection of terminals in the cell. Depending on the offeredtraffic in cell and the mutual interference coupling with thesurrounding cells, transmission/reception on all component carriers maynot always be the best solution. It is therefore proposed that each celldynamically selects additional component carriers fortransmission/reception as well. The latter is referred to as selectionof secondary component carriers (also some-times called extendedcarriers). All component carriers not selected for primary or secondaryare completely muted (uplink/downlink) and not used by the cell.

For autonomous selection of primary and secondary component carriers.Once a new LTE-Advanced (home) eNode-B is switched on, it shall start byselecting one of the component carriers as its primary. UEs can notconnect to the eNode-B before the primary carrier has been selected, andno signals are transmitted from it. The information available forselection of the primary component carrier is therefore mainly localeNode-B measurements (e.g. uplink received interference on eachcomponent carrier) as well as potential information from surroundingactive eNode-B on which component carriers they have selected. Once theeNode-B has selected its primary component carrier, it can start tocarry traffic. The quality of the primary component carrier ishere-after monitored by the eNode-B, and in case quality problems aredetected, it may trigger a reselection, where another component carrieris selected as the primary. As the offered traffic increases for thecell, the eNode-B starts to allocate additional secondary componentcarriers, if this can be allowed without seriously degrading theperformance of surrounding cells. Information available for secondarycarrier selection (or release in case of lower offered traffic) couldinclude both local eNode-B measurements, measurements from activeterminals attached to the cell, as well as limited side-information fromthe surrounding eNode-Bs. The latter may include information of whichcomponent carrier's different neighboring eNode-Bs have selected forprimary and secondary, as well as signaling to allow one eNode-B toindicate if it is experiencing severe quality problems on certaincomponent carriers.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

There is a need for some information exchange between neighboring nodesof systems as described above to allow for example convergence in theselection of the component carriers that results in the optimalfrequency re-use, conditioned on the offered traffic, etc. In order tobe able to fully accommodate such cases, an embodiment of the inventionuses over-the-air communication between eNode-Bs which may be within theLTE-Advanced system bandwidth. A possible solution for facilitating suchover-the-air communication between nodes could potentially be via abroadcast channel. Note that over-the-air communication also is expectedto be useful for other self optmised networks (SON) or like features,including during initialization and self configuration of new homeeNode-Bs that are powered on.

In one embodiment of the invention, there are designated timeslots, forexample timeslots arranged at regular (periodic) intervals, during thetimeslots, all Node Bs either listen to or transmit OTAC messages. FIG.5 shows one embodiment of how this embodiment may be implemented. Atregular intervals, timeslots 16 are designated for transmission and/orreception of OTAC messages between base stations. The periodicity of thetime slots may be in one example of an embodiment 100 ms. Theperiodicity may in one embodiment be fixed in the LTE-Advancedspecifications, or operator configurable via e.g. operation andmaintenance. In a preferred embodiment of the invention the designatedtimeslot interval may be the same for all Node Bs. In a preferredembodiment of the invention the pattern of timeslots for co-ordinationi.e. OTAC message TX/RX are a function of the system frame number (SFN).The system frame number is a counter that is running in each cell, andsimply counts the number of frames elapsed. This number is increasedevery time a frame has elapsed (10 ms in LTE). The value of the SFN isused for defining the discontinuous reception patterns (DRX) forinstance. In general, this SFN is used for any operation that requirestimed operation (like paging).

The invention is not limited to this scheme but other alternatives forproviding inter-Node B synchronisation of OTAC ‘openings’ are providedby the invention. In one embodiment the timeslots/intervals between themare based on GPS based timing. In another embodiment thetimeslots/intervals between them are based on home Node Bs monitoringand adopting to the patterns of neighbouring Node Bs. If a Node B has noOTAC messages to transmit, then it listens to potential OTAC messagescoming from other Node Bs, and try to decode those if such messages aresent.

In one embodiment, if a Node B has an OTAC to be transmitted, then itmay transmit the OTAC message in the first coming timeslot, instead oflistening to OTAC messages. In another embodiment there may be multipleOTAC resources

In one embodiment, the OTAC message is retransmitted after N OTACtime-slot periods, where N is a (pseudo) randomized integer, that isdifferent from each Node B. N may be picked randomly from a set ofpossible values, or it may be selected as a function of the cell ID(i.e. in that case the value of N will be different for cells that arein the same close vicinity).

The reason for sending the same OTAC message twice or more times atdifferent time-instances, is that some Node Bs may miss reception ofsuch an OTAC message, if at the same time transmitting own OTAC message.With randomized transmission of always retransmitting each OTAC message,the probability of this happing is significantly reduced.

The requirements for OTAC messages in embodiments of the invention is sosuch messages are sent with a low frequency from Node Bs, i.e. in theorder of every five to tens (on event basis). A periodicity of 100 ms(or more) of the time intervals for sending/receiving OTAC messages isconsidered to be sufficient.

The invention is implemented in one embodiment of the invention at theNode Bs only, and does not require any direct changes or support fromterminals. However, specifications in certain embodiments are updated inorder to allow timing for implicit channels to reflect the missing NodeB transmission times (to handle missing/delayed Ack/Nack for UL datachannels). The advantage of the invention is that it is fairly simple toimplement and provides sufficiently good performance.

The embodiments of this invention may be implemented by computersoftware executable by a data processor of the mobile device, such as inthe processor entity, or by hardware, or by a combination of softwareand hardware. Further in this regard it should be noted that any blocksof the logic flow as in the figures may represent program steps, orinterconnected logic circuits, blocks and functions, or a combination ofprogram steps and logic circuits, blocks and functions.

The foregoing description has provided by way of exemplary andnon-limiting examples a full and informative description of theexemplary embodiment of this invention. However, various modificationsand adaptations may become apparent to those skilled in the relevantarts in view of the foregoing description, when read in conjunction withthe accompanying drawings and the appended claims. However, all such andsimilar modifications of the teachings of this invention will still fallwithin the scope of this invention as defined in the appended claims.

The invention claimed is:
 1. A method of co-ordinating communicationbetween a plurality of base stations in a communication system, themethod comprising: at least one of designating and synchronisingtimeslots where said base stations receive and/or transmit informationto each other, wherein the information is retransmitted after Ntimeslots periods, where N is an integer and is different from andvaries between different base stations.
 2. A method as claimed in claim1, wherein the information is retransmitted after N timeslots periodswherein N is based on base station ID.
 3. A base station comprising: atleast one antenna for wireless communication, and a data processingentity connected with a memory that stores computer software, whereexecution of the computer software by the data processing entity resultsin the base station being configured to receive and/or transmitinformation to or from one or more other base stations during at leastone of designated and synchronised timeslots, wherein the information isretransmitted after N time-slot periods, where N is an integer and isdifferent from and varies to other base stations.
 4. A base station asclaimed in claim 3, wherein said information is over-the-aircommunication (OTAC) messages.
 5. A base station as claimed in claim 3,wherein timing of the timeslots is a function of system frame number(SFN).
 6. A base station as claimed in claim 3, wherein the base stationis part of an autonomous network.